Surface fluorination of F-containing resin molded article

ABSTRACT

Fluorine-containing resin molded article comprising a molded article of a fluorine-containing resin composition containing 0.1 to 30% by weight of a carbon material, a surface of said molded article being fluorinated. The fluorine-containing resin molded article can be obtained by, after preparing molded article of a fluorine-containing resin composition containing 0.1 to 30% by weight of a carbon material, fluorinating the surface of the article with a reaction gas which comprises a compound containing fluorine atom. This fluorine-containing resin molded article has an antistatic property and non-tackiness.

This application is a continuation of application Ser. No. 08/525,625filed Sep. 22, 1995 which has been abandoned.

TECHNICAL FIELD

The present invention relates to a fluorine-containing resin moldedarticle having an excellent antistatic property and non-tackiness and toa process for preparation of the same.

The present invention also relates to a fixing roller for anelectrostatic copying machine having a high toner-offset-preventingability, which comprises the provision of a sheet or film of afluorine-containing resin composition on the outer surface of a metalroller.

BACKGROUND ART

Fluorine-containing resins such as homopolymer or copolymers oftetrafluoroethylene have a very low surface energy in comparison withother resins, and therefore have an extremely superior surfaceproperties such as water- and oil-repelling property, non-tackiness andmold-releasing property. In addition, it has been known that because oftheir chemical stability, they have many excellent properties such aschemical resistance, corrosion resistance and heat resistance, and thusthe fluorine-containing resins have been applied to wide and variousfields.

The fluorine-containing resins, however, have problems that they areeasy to be electrostatically charged, because they are electricallyinsulative.

For example, in computer devices and various office automation (O.A.)machines, electronic parts such as IC and LSI and magnetic storages mustbe protected from electrostatic charge and sparks due to the charge.Therefore, for the parts to be used for their peripheral equipments orbusiness machines (e.g. bearing parts for various rollers andtransferring machines) are required a sufficient antistatic property.

Further, for a reservior of chemicals and an equipment used inpreparation process of semiconductors, but for a sufficient antistaticproperty, not only the elements are broken due to the electrostaticcharge, but also the maintenance of clean environment is obstructed.

Moreover, a fluorine-containing resin film is used as anoffset-preventing layer for the surface of a fixing roller in a heatroller fixing equipment of electrostatic copying machines. In this case,when using the fluorine-containing resin alone, though non-tackiness andmold-releasing property to a toner melted by heating (hereinafterreferred to as "hot-offset-preventing effect") are sufficient, therearises the problem of a phenomenon so-called electrostatic offset, thatis, due to the abrasion between the fixing roller and paper sheets theoffset-preventing layer of the fluorine-containing resin is chargedgradually, and then the toner before fixing is electrostaticallyadsorbed or repelled, which results in blotting and missing inelectrostatic images.

Further, in view of saving energy and shortening a warm-up time ofmachines it is desired to carry out the fixing at a temperature as lowas possible. For this purpose, a fixing roller having an excellent heatconductivity is desired. Accordingly, it is required that theoffset-preventing layer is made as thinner as possible and also hasabrasion resistance together with the above various properties.

In order to solve the above problems, there has been proposed acomposition of a fluorine-containing resin with which variouselectrically conductive fillers are blended.

For example, JP-B-38302/1991 discloses a fluorine-containing resincomposition to which a carbon black is added as the electricallyconductive filler. When adding the electrically conductive carbon blackto the fluorine-containing resin, the composition is endowed with anelectric conductivity and thus an excellent antistatic ability can beachieved. However, since the electrically conductive carbon black has alarger surface energy than the fluorine-containing resin, the carbonblack is inferior to the fluorine-containing resin in such properties aswater- and oil-repelling property, non-tackiness and mold-releasingproperty. Accordingly, the composition of the fluorine-containing resinand the electrically conductive carbon black has the problem that thecomposition is inferior to the fluorine-containing resin used alone insuch properties as water- and oil-repelling, non-tackiness andmold-releasing property, and therefore such a composition has beenpractically used within the limited use.

To the offset-preventing layer of the fixing roller, it has been alsotried to add various electrically conductive fillers.

For example, JP-B-23626/1983 proposes the use of a resin layercontaining a carbon black and the like as the offset-preventing layer.When an addition amount of carbon black is made larger, a volumespecific resistivity can be lowered, which results in improvement ofelectrostatic offset-preventing effect. However, the hotoffset-preventing effect becomes bad. In order to solve this dilemma, inthe practical application there is obliged to use a wet process in whicha silicone oil is applied to the surface of the fixing roller.

JP-B-59468/1990 proposes the addition of a carbon fluoride to afluorine-containing resin together with a carbon fiber as theelectrically conductive filler in order to compensate the hotoffset-preventing effect. In this case, though the both offsets, i.e.hot-offset and electrostatic-offset can be prevented, it is difficult toform uniformly an offset-preventing layer containing the two fillers.When the surface of the offset-preventing layer is uneven, it isimpossible to maintain the offset-preventing effect for a long time.

As explained above, in the practical situation, it is difficult toprepare a fluorine-containing resin molded article which has a uniformsurface and is simultaneously sufficient in both of antistatic abilityand non-tackiness.

The present invention has been made on the basis of those problems, andhas an object to provide a fluorine-containing resin molded article withan excellent antistatic ability and non-tackiness due to its properelectric conductivity and sufficiently low surface energy.

Another object of the present invention is to provide a novel processfor preparing a fluorine-containing resin molded article with anantistatic ability and non-tackiness.

Further object of the present invention is to provide a fixing rollerfor electrostatic copying machine having a high offset-preventingability, and to provide a preparation process of the same.

DISCLOSURE OF THE INVENTION

The present invention relates to a fluorine-containing resin moldedarticle, comprising a molded article of a fluorine-containing resincomposition containing 0.1 to 30% by weight of a carbon material, asurface of said molded article being fluorinated.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, the fluorine-containing resin is used as amatrix. Examples of the fluorine-containing resin are, for instance,polytetrafluoroethylene, a copolymer of tetrafluoroethylene with atleast one of other copolymerizable ethylenically unsaturated monomers(for example, olefins such as ethylene and propylene, halogenatedolefins such as hexafluoropropylene, vinylidene fluoride,chlorotrifluoroethylene and vinyl fluoride, perfluoro(alkyl vinylethers), and the like), polychlorotrifluoroethylene, poly(vinylidenefluoride), and the like. The particularly preferable fluorine-containingresin among them is polytetrafluoroethylene, a copolymer oftetrafluoroethylene with at least one of hexafluoropropylene,perfluoro(methyl vinyl ether) and perfluoro(propyl vinyl ether) (whichis contained in an amount of not more than 40% by mole totetrafluoroethylene), and the like. Also, the fluorine-containing resinmay be used in a mixture of two or more as well as used alone.Particularly preferable mixture is a mixture of polytetrafluoroethyleneand a copolymer of tetrafluoroethylene with perfluoro(alkyl vinylether), and the like.

In the present invention, the carbon material is added as anelectrically conductive filler. Examples of the carbon material are, forinstance, carbon black, graphite powder, carbon fiber, sphericalglass-like carbon, meso-carbon microbeads, and the like. If necessary,these may be heat-treated at 1,000° C. to 3,000° C. Particularlypreferable carbon material is a carbon black which is classified as theelectrically conductive carbon black. For example, there may be usedKetjen Black EC (tradename) and Ketjen Black EC-600 JD (tradename) fromLION-AKZO, VULCAN XC-72 (tradename) and Black Pearls 2000 (tradename)from Cabot Corporation, HS-500 (tradename) from Asahi Carbon, DenkaBlack (tradename) from Denki Kagaku Kogyo, and the like.

An amount of the carbon material to be added to the fluorine-containingresin is properly 0.1 to 30% by weight. When less than 0.1% by weight, asufficient electric conductivity cannot be obtained, and when more than30% by weight, the abrasion resistance undesirably becomes worse and themechanical strength becomes lowered.

In the present invention, the fluorine-containing resin molded articlecan be produced by preparing a molded article of a fluorine-containingresin composition containing 0.1 to 30% by weight of the carbonmaterial, and then fluorination-treating the surface of the article witha reaction gas of a compound containing fluorine atom. The moldedarticle is prepared in the shape of rod, block, board, cup, cylinder,sheet, film, and the like.

A process for preparing a molded article having a desired shape bymixing the fluorine-containing resin and the carbon material is notparticularly limited, and an adequate process can be optionally employeddepending on the materials.

For instance, as a process for preparing a cup-like or cylindricalmolded article there may be employed a process in which after mixingwith agitation the fluorine-containing resin powder and the carbonmaterial powder, the mixed powder is press-molded and heat-treated; aprocess in which the mixed powder is melted and is subjected toinjection molding, and the like. As a process for preparing a sheet orfilm, there may be employed a process in which the fluorine-containingresin and the carbon material are dispersed into an aqueous solution towhich a surfactant and the like is optionally added, and the dispersionis applied in wet system on a proper substrate, then dried andheat-treated; a process in which a composite fine particle material isprepared from the florine-containing resin and the carbon material andis subjected to powder coating, then heat-treated to form a film, andthe like. In any molding process, after the molding, a certain processstep such as washing or polishing may be added, if necessary.

In the present invention, the reaction gas comprising a compoundcontaining fluorine atom (hereinafter referred to as"fluorine-containing reaction gas") which is used in the fluorinationtreatment is, for instance, fluorine gas, nitrogen trifluoride gas,chlorine trifluoride gas or sulfur tetrafluoride gas, and these gasesmay be optionally diluted with an inert gas such as nitrogen gas. Inaddition, those gases may be used in an admixture, and if necessary,oxygen gas, steam or hydrogen fluoride gas may be added thereto.

The temperature of the fluorination treatment varies with kinds of thereaction gases, kinds of the fluorine-containing resins, kinds of thecarbon materials, and form, thickness or composition of the moldedarticles or films, and is in the proper range from 50° to 350° C.,particularly from 100° to 250° C. A proper treating time is from 1minute to 5 hours, particularly from 30 minutes to 2 hours. When thetreating temperature is lower than 50° C., the reaction which producesC--F bond cannot substantially proceed by the fluorination treatmentwith the fluorine-containing reaction gas, and thus an effectivetreatment is impossible. When higher than 350° C., thefluorine-containing resin is deformed and thermally decomposed as wellas a degree of fluorination tends to become excess and an electricresistance tends to be larger, which results in inconvenience.

The degree of fluorination treatment is determined by a degree offluorination at the surface. In the present invention, the degree ofsurface fluorination is defined by the value measured by the followingmanner.

F_(1S) spectrum (880 to 700 eV) and C_(1s) spectrum (280 to 300 eV) of afluorine-containing resin molded article are measured with X rayphotoelectron spectrometer (ESCA-750 of Shimadzu Corporation). From aratio of areas in the charts corresponding to each spectrum, a ratio F/Cof the number of fluorine atoms to the number of carbon atoms at thesurface of the carbon fluoride particle is calculated. This value is thedegree of surface fluorination. A value of the degree of surfacefluorination varies with kinds of the fluorine-containing resins used,and is properly from around 1.0 to 3.0, particularly around 2.0 to 3.0.

Since the surface of the fluorine-containing resin molded article issubjected to the fluorination treatment, the molded article has anenriched surface lubricity and is excellent in abrasion resistance.

Prior to the above-mentioned fluorination treatment by using thefluorine-containing reaction gas, according to the present invention, atleast the surface of the molded article can be subjected topre-oxidation treatment.

As the pre-oxidation in the present invention, there may be employedgas-phase oxidation method, liquid-phase oxidation method orelectrolytic oxidation method.

According to the gas-phase oxidation method, for example, a gas such asoxygen gas, ozone, nitrogen oxide or steam is contacted with the surfaceof the molded article or film at a temperature within the preferredrange of 100° to 350° C. A reaction temperature varies with kinds of thegases, concentrations of the gases, kinds of the fluorine-containingresins, kinds of the carbon materials, or form, thickness or compositionof the molded articles or films, and properly is 100° to 350° C. Whenlower than 100° C., the pre-oxidation gives an insufficient effect, andwhen higher than 350° C. the fluorine-containing resin is inconvenientlydeformed or thermally decomposed.

According to the liquid-phase oxidation method, for example, the moldedarticle or film is dipped in a chemical solution of nitric acid,permanganate/sulfuric acid, a chromate, a hypochlorite, or the like.

In the liquid-phase oxidation method, when using, for example, aconcentrated sulfuric acid, the method is feasible by boiling for 0.5 to6 hours.

According to the electrolytic oxidation method, the molded article orfilm to be treated is set as a cathode in 1N sulfuric acid solution, anda direct voltage of 1 to 50 V is applied thereto.

Among them, the gas-phase oxidation method is particularly preferable,because the method can be carried out in the same reactor as for thefluorination treatment to be conducted afterwards, which can simplifythe process steps, and further remarkable effects can be obtained.

When the conditions of the fluorination treatment are optimized, themolded article comprising the fluorine-containing resin and the carbonmaterial can be fluorinated only at the surface layer, and the innerpart can be maintained in non-fluorinated state.

In, the fluorinated surface layer, an extremely excellent low surfaceenergy can be exhibited, because the carbon material is converted intothe carbon fluoride at its surface. Therefore, improvement of water- andoil-repelling property, mold-releasing property and non-tackiness can beaccomplished in comparison with the sole use of the fluorine-containingresin. In addition, lubricity and abrasion resistance are improved. Ingeneral, it is known that a fluorine-containing resin contains terminalstructures derived from an initiator or a chain transfer agent which areused in polymerization. For example, in many cases the resin has the endgroups such as --COOH end goup and --CONH₂ end group, and those groupsare polar group which is a factor to make a surface energy of thefluorine-containing resin larger.

JP-A-25008/1991 discloses that those polar end groups can be convertedinto --CF₃ by treating with fluorine gas.

According to the present invention, since only in the surface layerthose polar end groups are converted into --CF₃ end group by thefluorination treatment, the surface energy can be synergisticallylowered together with the production of the carbon fluoride, and thus amolded article having an extremely superior water- and oil-repellingproperty, mold-releasing property and non-tackiness.

On the other hand, since the electrically conductive carbon material isconverted into the insulative carbon fluoride by the fluorinationtreatment, there is anxiety that the electric conductivity of the moldedarticle becomes lower. However, since only the very limited area of thesurface layer is subjected to the fluorination treatment, the increasein volume specific resistivity is very little. As a result, the moldedarticle which can satisfy both the electric conductivity andnon-tackiness can be obtained.

Further, when the oxidation treatment is carried out prior to thefluorination treatment, the fluorination treatment can be carried outunder gentle conditions and uniformly, which can prevent the moldedarticle from deforming and being rough.

With respect to this effect, though details are not known, the reasonsare assumed as follows. Namely, it is said that an oxidized graphiteprepared by oxidizing a carbon material is fluorinated at a temperaturelower than that of fluorination treatment of the original carbonmaterial to produce a fluorinated graphite (carbon fluoride) (e.g.Summary of Symposium in 15th Fluorine Chemistry, pp. 16-17, 1990).Accordingly, in the present invention, the surface or whole of thecarbon material has an oxidized graphite-like structure by the oxidationtreatment, and the fluorination can be carried out under more gentleconditions.

In another aspect, it is known that an anode effect which is obtained bycoating a surface of carbon electrode with a carbon fluoride film influorine generating electrolysis, can scarcely be obtained in theabsence of water, but can easily be obtained in the presence of a traceamount of water (e.g. Journal of Fluorine Chemistry, Vol. 57, pp.83-91(1992)). It is assumed that this phenomenon shows the fact that thetrace amount of water or the atomic oxygen produced by the electrolyticoxidation can assist the production of the carbon fluoride film.Therefore, in the fluorination treatment of the present invention, it isassumed that the production of carbon fluoride is accelerated by theoxidation treatment such as steam treatment prior to the fluorinationtreatment.

With respect to the fluorine-containing resin, when the oxidationtreatment such as steam treatment is carried out prior to thefluorination treatment, the polar end groups can be more easilyconverted into --CF₃ end group. Namely, as mentioned above, it is knownthat the polymer end of the fluorine-containing resin has variousstructures, and in some cases the end group is --COF. This --COF endgroup is difficult to be converted into --CH₃ end group by simply beingsubjected to the fluorination treatment with fluorine gas, and severereaction conditions and a longer reaction time are required. Accordingto the steam treatment, however, the --COF end group can easily beconverted into --COOH end group, and the --COOH end group can easily beconverted into --CF₃ end group by the treatment with fluorine gas.

Therefore, the oxidation treatment is effective to the fluorination ofthe end groups of the fluorine-containing resin.

As mentioned above, by carrying out the oxidation treatment with steamor proper oxidizing agents prior to the fluorination treatment, thefluorination treatment can be carried out effectively under more gentleconditions. This is relating to modification of both thefluorine-containing resin and the carbon material. By such mutualeffects, the fluorine-containing resin molded article having anexcellent electric conductivity and non-tackiness can be effectivelyobtained.

The fluorine-containing resin molded article of the present invention isused for rollers of an electrostatic copying machine such as a fixingroller, a transferring roller, a paper feeding roller and a conveyingroller; bearings thereof. Further, the molded article can be applied forvarious uses, e.g. a reservior or tray for chemicals used insemiconductor preparation process, a casing for conveying or keepingwafers and electronic parts such as IC, a heating element, anelectromagnetic wave shielding material, and the like.

For example, when the above-mentioned fluorine-containing resin film isformed on an outer surface of a metal roller, the obtained roller is afixing roller for an electrostatic copying machine having a veryexcellent offset-preventing effect.

That is, the present invention relates to a fixing roller for anelectrostatic copying machine, comprising a metal roller on which outersurface is provided with a sheet or film which is prepared byfluorinating a surface of a molded article of a fluorine-containingresin composition comprising 0.1 to 30% by weight of carbon material.

The metal roller of the fixing roller according to the present inventionmay be made of materials having an excellent heat conductivity anddimension stability as well as being light, e,g, aluminium or stainlesssteel.

The fluorine-containing resin in the fixing roller according to thepresent invention is the same as mentioned above, and is particularlypreferably a copolymer of tetrafluoroethylene and perfluoro(alkyl vinylether), or a mixture of polytetrafluoroethylene and a copolymer oftetrafluoroethylene and perfluoro(alkyl vinyl ether).

The offset-preventing layer in the fixing roller according to thepresent invention may be formed by usual known methods in which afluorine-containing resin layer containing a carbon material is used asthe offset-preventing layer. Among them, in view of easiness, there isproperly employed a method in which a mixed dispersion of thefluorine-containing resin and the carbon material is applied to thesurface of the metal roller, dried and then sintered. After the filmformation, it is possible to increase a surface roughness by sanding.

The fixing roller of the present invention is produced by, after theformation of the offset-preventing layer, carrying out the fluorinationtreatment according to the above-mentioned method. Prior to thefluorination treatment, when the above-mentioned steam treatment oroxidation treatment is carried out, the fixing roller can exhibit moreexcellent offset-preventing ability.

The present invention is explained below on the basis of Examples, andthe present invention is not limited to the Examples.

EXAMPLE 1

Molding pellets were prepared by mixing uniformly 20 parts by weight ofa pitch-type carbon fiber (M-107T from Kureha Chemical Co., Ltd., fiberlength: 700 μm, aspect ratio: 39) and 80 parts by weight oftetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer (PFA) powder(Neoflon PFA AP210 from Daikin Industries, Ltd.) with Henshel mixer, andthen melting and kneading at 350° to 370° C. by a biaxial extruder withtwo screws rotating in a different direction.

The obtained pellets were fed to an injection molding machine (cylindertemperature: 350° to 380° C., die temperature: 180° C.) to prepare adisc-like test piece (diameter: 12 cm, thickness 0.5 cm) by injectionmolding.

A reactor of monel (capacity. 1.5 liters) was charged with the obtainedtest piece and sealed, and then a pressure was reduced to 1 Pa or lowerby a vacuum pump. After heating the reactor to 200° C., a high puritynitrogen gas was passed though at 1 l/min for one hour to sufficientlydry the test piece, and then the fluorination treatment was carried outby passing a 20% fluorine gas diluted with nitrogen gas at 1 l/min at200° C. for 2 hours. Immediately after the completion of thefluorination treatment, while passing a high purity nitrogen gas at 1l/min, the test piece was cooled to room temperature and then taken out.

With respect to the test piece, a contact angle to water and a volumespecific resistivity (measured by using R8340A Digital SuperhighResistivity Meter and R12702A Resistivity Chamber available fromKabushiki Kaisha Advantest) were measured. The results are shown inTable 1.

EXAMPLE 2

A disc-like test piece of the PFA resin containing the pitch-type carbonfiber as a filler was prepared in the same manner as in Example 1.

This test piece was sealed in a reactor of monel (capacity: 1.5 liters),and a temperature was raised to 200° C. with passing a high puritynitrogen gas at 1 l/min.

Subsequently, while maintaining a temperature of the reactor at 200° C.,a nitrogen gas containing steam was passed through the reactor at 1l/min to previously oxidize the test piece, an amount of said steam inthe nitrogen gas being equal to the saturated amount at 30° C.

After that, the fluorination treatment was carried out by passing a 20%fluorine gas diluted with nitrogen gas at 1 l/min at 200° C. for onehour. Immediately after the completion of the fluorination treatment,while passing a high purity nitrogen gas at 1 l/min, the test piece wascooled to room temperature and taken out.

The obtained test piece was evaluated in the same manner as inExample 1. The results are also shown in Table 1.

COMPARATIVE EXAMPLE 1

Evaluation of the contact angle to water and the volume specificresistivity was carried out in the same manner as in Example 1 withrespect to the test piece of the PFA resin containing the pitch-typecarbon fiber as a filler, which was prepared in Example 1 but was notsubjected to the subsequent treatments such as the fluorinationtreatment. The results are shown in Table 1.

COMPARATIVE EXAMPLE 2

A test piece was prepared in the same manner as in Example 1 except that15 parts by weight of the pitch-type carbon fiber and 5 parts by weightof a carbon fluoride (CFGL from Daikin Industries, Ltd.) were usedinstead of 20 parts by weight of the pitch-type carbon fiber and thatthe fluorination treatment was not carried out. The evaluation wasconducted in the same manner as in Example 1. The results are shown inTable 1.

                  TABLE 1    ______________________________________                          Volume specific              Contact angle to water                          resistivity              (degree)    (Ω · cm)    ______________________________________    Ex. 1       136           4 × 10.sup.9    Ex. 2       141           5 × 10.sup.8    Com. Ex. 1  123           2 × 10.sup.7    Com. Ex. 2  125           3 × 10.sup.9    ______________________________________

EXAMPLE 3

To a PFA resin solution (Polyfulon Dispersion AD-1CR from DaikinIndustries, Ltd.) was added an electrically conductive carbon (KetjenBlack EC from LION AKZO) in an amount of 20% by weight to the solidcontent of the PFA resin solution, and sufficiently mixed and dispersedby means of an ultrasonic homogenizer.

A surface of an aluminium roller (outer diameter: 50 mm, inner diameter:44 mm, length: 350 mm) was roughened by means of sandblast treatment,and thereto the above mixed dispersion was applied uniformly byair-spraying, and then the roller was subjected to heat treatment in ahot-air circulation type thermostatic oven of 380° C. for one hour.

Subsequently, the aluminium roller was put in a reactor of monel(capacity: 10 liters) and then sealed, and a high purity nitrogen gaswas passed therethrough at 5 l/min for one hour, then the reactortemperature was raised to 200° C. After the temperature reached theequilibrium state, the fluorination treatment was carried out by passinga 20% fluorine gas diluted with nitrogen gas at 2 l/min at 200° C. for 2hours. Immediately after the completion of the fluorination treatment,while passing a high purity nitrogen gas at 5 l/min, the aluminiumroller was cooled to room temperature and taken out.

A fixing portion of electrostatic copying machine was equipped with thisroller, and properties of the roller were evaluated with respect tonon-offset region property, charging property at paper passing andabrasion resistance.

The non-offset region property was measured by actually passing foursheets of paper of A4 size while changing a temperature of the heatedfixing roller in 10° C. steps. The results were evaluated by observingwith naked eyes as to whether missing or bleeding of letters occurred ornot, and are shown by a temperature region where no offset occurred.

The charging property at paper passing was evaluated by measuring asurface potential of the fixing roller upon the above-mentionedpaper-passing test by means of a vibration reed-type surfacepotentiometer (340 HV from Treck Japan).

The abrasion resistance was evaluated by measuring an abrasion amount(reduced amount: μm) after passing fifty thousand sheets of paper of A4size.

EXAMPLE 4

An aluminium roller coated with the PFA film containing the electricallyconductive carbon was prepared in the same manner as in Example 3.

The aluminium roller was put in a reactor of monel (capacity: 10 liters)and then sealed, and a high purity nitrogen gas was passed therethroughat 5 l/min, then the reactor temperature was raised to 200° C.Subsequently, while maintaining a temperature of the reactor at 200° C.,a nitrogen gas containing steam was passed through the reactor at 2l/min to previously oxidize, an amount of said steam in the nitrogen gasbeing equal to the saturated amount at 30° C.

After that, the fluorination treatment was carried out by passing a 20%fluorine gas diluted with nitrogen gas at 1 l/min at 200° C. for onehour.

Immediately after the completion of the fluorination treatment, whilepassing a highly pure nitrogen gas at 2 l/min, the roller was cooled toroom temperature and taken out.

The obtained roller was evaluated in the same manner as in Example 3.The results are shown in Table 2.

COMPARATIVE EXAMPLE 3

The same evaluation as in Example 3 was conducted with respect to thealuminium roller coated with the PFA film containing the electricallyconductive carbon prepared in Example 3 which was not subjected to thesubsquent treatments such as the fluorination treatment. The results areshown in Table 2. This roller has a smallest charging potential becausethe electrically conductive carbon is contained. However, since thesurface energy is larger than that of the PFA alone, the hot-offseteasily occurs and the non-offset region becomes narrower.

COMPARATIVE EXAMPLE 4

A roller was prepared in the same manner as in Example 3 except that,instead of the electrically conductive carbon, the pitch-type carbonfiber (the same as used in Example 1) and the carbon fluoride (the sameas used in Comparative Example 3) were added in amounts of 15% by weightand 5% by weight to the solid content of the PFA resin solution,respectively, and that the fluorination treatment was not carried out.The evaluation was conducted in the same manner as in Example 3. Theresults are shown in Table 2.

                  TABLE 2    ______________________________________                        Charging  Abrasion            Non-offset region                        potential amount    ______________________________________    Ex. 3     150° to 230° C.                             0 to -130 V                                      1 to 2 μm    Ex. 4     150° to 240° C.                            0 to -50 V                                      1 to 2 μm    Com. Ex. 3              160° to 210° C.                            0 to -50 V                                        12 μm    Com. Ex. 4              150° to 200° C.                            0 to -50 V                                      2 to 3 μm    ______________________________________

The fluorine-containing resin molded article of the present invention isexcellent in antistatic property, mold-releasing property andnon-tackiness because of its very low surface energy and its electricconductivity.

The process of the present invention is widely applicable, since thegas-phase treatment is carried out after molding to a desired shape,which does not restrict shape of molded articles.

According to the fixing roller of the present invention, the hot-offsetand the electrostatic-offset scarcely occur. Further, since there is noprocess step where a composition containing a carbon fluorine is molded,it is possible to make the offset-preventing layer thinner and moreuniform, and also the cold-offset may not occur. In addition, since thesurface lubrication is good, the abrasion resistance becomes excellent,which makes its life longer.

INDUSTRIAL APPLICABILITY

The fluorine-containing resin molded article of the present invention isusable for rollers of an electrostatic copying machine such as a fixingroller, a transferring roller, a paper feeding roller and a conveyingroller; bearings thereof. Further the molded article can be applied forvarious uses, e.g. a reservior or tray for chemicals used insemiconductor preparation process, a casing for conveying or keepingwafers and electronic parts such as IC, a heating element, anelectromagnetic wave shielding material, and the like.

We claim:
 1. A fluorine-containing resin molded article, comprising amolded article of a fluorine-containing resin composition containing 0.1to 30% by weight of a carbon material, a surface of said molded articlebeing fluorinated with heating at a temperature of from 100° C. to 250°C. with a reaction gas selected from the group consisting of a compoundcontaining fluorine atom and a mixed gas of the compound containingfluorine atom and an inert gas.
 2. The fluorine-containing resin moldedarticle of claim 1, wherein the fluorine-containing resin is at leastone selected from the group consisting of polytetrafluoroethylene, acopolymer of tetrafluoroethylene with at least one of othercopolymerizable ethylenically unsaturated compound monomers,polychlorotrifluoroethylene and poly(vinylidene fluoride).
 3. Thefluorine-containing resin molded article of claim 1 wherein the articleis in the form of rod, block, plate, cup, cylinder, sheet or film.
 4. Aprocess for preparing a fluorine-containing resin molding article, whichcomprises after preparing a molded article of a fluorine-containingresin composition containing 0.1 to 30% by weight of a carbon material,a step for fluorinating the surface of the article with heating at atemperature of from 100° C. to 250C. with a reaction gas selected fromthe group consisting of a gas of a compound containing fluorine atom anda mixed gas of the compound containing fluorine atom and an inert gas.5. The process for preparing the fluorine-containing resin moldedarticle of claim 4, wherein the fluorine-containing resin is at leastone selected from the group consisting of polytetrafluoroethylene, acopolymer of tetrafluoroethylene with at least one of othercopolymerizable ethylenically unsaturated compound monomers,polychlorotrifluoroethylene and poly(vinylidene fluoride).
 6. Theprocess for preparing the fluorine-containing resin molded article ofclaim 4 wherein the article is in the form of rod, block plate, cup,cylinder, sheet or film.
 7. A fixing roller for an electrostatic copyingmachine, comprising a metal roller, an outer surface of which isprovided with a sheet-like or film-like fluorine-containing resin moldedarticle of claim
 3. 8. The fluorine-containing resin molded article ofclaim 2, wherein the article is in the form of rod, block, plate, cup,cylinder, sheet or film.
 9. The process for preparing thefluorine-containing resin molded article of claim 5, wherein the articleis in the form of rod, block plate, cup, cylinder, sheet or film.
 10. Afluorine-containing resin molded article having improved anti-staticproperties and non-tackiness made of a fluorine-containing resincomposition consisting essentially of 0.1 to 30% by weight of anelectrically conductive carbon filler and a remainder of saidfluorine-containing resin, a surface of said molded article beingfluorinated.
 11. The fluorine-containing resin molded article of claim10, wherein carbon fluoride is present only in said surface of saidmolded article, and end groups of said fluorine-containing resin in saidsurface are converted into CF₃ by said surface being fluorinated.